Espar makes a tankless diesel fired heater that will run with your heat exchanger and service all your heat and hot water needs.Very compact and economical to run fuel wise and power drain wise. Not a cheap system but fits every requirement I would want on my sailboat.

That's a good suggestion, but would kibosh the ESPAR idea and go with the Webasto version as Espar is known for poor reliability and support.

In Hal Roth's book "How to Sail Around the World" he says that his wife and himself simple used a pump sprayer he modified with a nozzle from a kitchen sink. They would just boil a certain amount of water and pour it into the sprayer with some cool water. Then they would just pump up the sprayer with some pressure and shower. This way they were able to take hot showers and conserve water. I thought the book was great. It is just packed with information like that.

I used one of those for many years. I found it preferable to solar cos you can control the heat but thats about all.

On Raven, our previous boat, I went one step further, mixing the hot/cold in a bucket or head basin then dropping one of those cheap 12v shower gizmos you can but at any chandlery. We could use either kettle or solar to heat the water. Worked well and with some simple plumbing you could make it a more permanent installation.

That said, I love our tank heater shower on the current Womboat. Sheer bliss, other than (as per previous quite) having to run the engine to heat the water.

The way we work it, is that we have a six gallon heater that is engine/electric. We run the engine rarely to charge the batteries and heat water. Do them both concurrently to save diesel. Although we have solar, a good charge twice a week with the diesel at idle is a help. Sponge baths between times. This is our plan when we want to conserve. While on shore power, we bathe at the marina or switch on the electric side.

We consider the six gallon tank to be additional water storage, so it's not wasted space.

Instantaneous propane heaters were practical and popular. The problem was safety. If not properly installed or operated there is a risk of the exhaust fumes getting into the cabin area. As a result most manufactures eliminated those lines for boats. They still make them for RVs where venting is easy. some also say their units can be used on boats. I still have my old unit and will be looking for a replacement

I replaced a gas-fired Wolter demand heater with a more conventional Isotemp heater in 1999. The Wolter unit had been notoriously unreliable and wasted a lot of water, even after having the Wolter folks upgrade the ignition system. I recall that this type of heater was implicated in carbon monoxide poisoning--including deaths. Mine was installed in the engine compartment that was ventilated by a blower when the heater was in use.

I am much more comfortable with the conventional water heater, which is a pretty basic piece of equipment. A demand heater, by comparison, is a complex piece of gear with more parts waiting to break.

Those of you that have larger boats with central ac. You can have your hvac tech install a High pressure hi temp gas to water heat exchanger on the discharge (high side) of the ac compressor/s R-22 and 410A both have pretty high temps that are well above 100* This would NOT serve as on demand. The logic against this idea is.. "well if I'm at dock using Electric for the AC then why not just use the electric WH. But, there are always bragging rights I guess Now, if your boat has an on board generator the reduced load by pre cooling the refrigerant will lower the ac's amp draw and also reduce or eliminate the amps required for the electric element in the WH. Jus a few words from your friendly neighborhood hvac lady

ps: this would work best on 24,000 btu ac or larger. smaller ones would not be worth the trouble of breaking into the refrigerant circuits.

This may be a small tangent, but, another point to consider is the use of a diversion load from a solar/wind charge controller. This diversion load circuit can include a 12v heating element installed in the hot water tank in place of the 110v element. Once the charge controller satisfies the battery banks, it diverts usable voltage to the diversion load. This is something I am considering but have not yet tried or even fully investigated. How efficient is this (no idea)???....but it does seem logical not to waste the electrical potential when available.

Here's an alternative. Buy a new garden pressure sprayer (not an old one that has held poisons), heat the water on the stove or whatever means you have, and you have a shower wand. If you don't have a shower stall in the head, it can be used on deck or whatever. We also installed a sink sprayer in the cockpit, hooked into the pressure water system. After a swim, all we need is a fresh water rinse.

On those rare occasions when we have a large crew out for a weekend, we supplement our domestic hot water supply with a sun shower. You can get 2-3 adult showers from a 4-5 gal bag, which is a lot better than we get with our pressure system.

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